The number 21020
21020 is a composite number with 12 divisors. Its prime factorisation is × 5 × 1051. Divisors (12): 1, 2, 4, 5, 10, 20, 1051, 2102, 4204, 5255, 10510, 21020.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21020: a Harshad number: divisible by its digit sum 5.
- 2
21020 is composite. Its prime factorisation is
- 3
The divisors add up to 44184; without 21020 itself that is 23164, so 21020 is abundant (23164 is more than 21020). Euler's totient φ(21020) = 8400 numbers up to 21020 share no factor with it.
- 4
The digits of 21020 add up to 5, and repeating that until one digit is left gives the digital root 5. The Collatz sequence (halve if even, else 3n+1) takes 87 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21020 = 2^{2} \times 5 \times 1051 \]21020 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 12 |
| Sum of divisors | 44184 |
| Euler totient φ(n) | 8400 |
| Square | 441840400 |
| Cube | 9287485208000 |
| Square root | 144.982758 (= 2√5255) |
| Digit sum / digital root | 5 / 5 |
| Collatz steps to 1 | 87 |
| Scientific notation | 2.102 × |
21020 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand and twenty |
| Binary (base 2) | 101001000011100 |
| Octal (base 8) | 51034 |
| Hexadecimal (base 16) | 521C |
| Base 3 | 1001211112 |
| As time | 21020 seconds = 5 h 50 min 20 s |
Is 21020 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21020 ÷ 2 = 10510) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | No (remainder 2) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | Yes (21020 ÷ 4 = 5255) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (21020 ÷ 5 = 4204) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 2) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 6) | A number is divisible by 7 if double the last digit and subtract it from the rest: the result is a multiple of 7. |
| 8 | No (remainder 4) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 5) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | Yes (21020 ÷ 10 = 2102) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 10) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 8) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21020 a prime number?
No. 21020 = × 5 × 1051, so it is divisible by 2.
What are the factors of 21020?
1, 2, 4, 5, 10, 20, 1051, 2102, 4204, 5255, 10510, 21020.
What is 21020 in binary?
101001000011100 (hexadecimal 521C, octal 51034).
What is the square root of 21020?
About 144.9828, exactly 2√5255.
Is 21020 divisible by 3?
No. Its digits add up to 5, which is not a multiple of 3.
What is special about the number 21020?
21020 is a Harshad number: divisible by its digit sum 5.